1. Field of the Invention
The present invention generally relates to power measurements and, more particularly to true Root Mean Square (“RMS”) power measurements of signals.
2. Related Art
In communication devices and signal processing applications, power measurements of time varying signals are frequently made. One type of power measurement measures the average power or RMS of a signal, which may be obtained by integrating the square of the signal over an integration interval and then dividing this integral by the integration interval.
An important performance metric of power measurement devices is the accuracy of the power measurements over a dynamic range of the signal. In a conventional RMS power measurement device, this measurement accuracy may be limited by the sensitivity of the device to variations in device process, voltage, or temperature (PVT). The measurement accuracy may also depend on the length of the integration interval, which is frequently a function of the statistics of the signal to be measured. Therefore, it is often desirable to change the integration interval to obtain a desired measurement accuracy. A conventional power measurement device may use a capacitor to change an integration interval. However, such a capacitor is often too big to be integrated into the power measurement device, making any change to the integration time difficult and costly. Furthermore, many power measurement devices generate power measurements as analog signals, so that extra circuitry is needed to obtain digital outputs required for subsequent processing. Such circuitry not only incurs extra cost but may also be subject to PVT variations, compounding the PVT sensitivity of the power measurement devices. Accordingly, there is a need for power measurement devices whose measurement accuracy is independent of PVT variations, whose integration interval is easily configurable, and whose output is digital.